Gas seals have been adapted for use on pumps particularly to create a sealed relationship between the rotatable pump shaft and the surrounding pump housing. The gas seal, which may be a single or double unit, typically employs a pressurized barrier gas which is supplied adjacent one periphery of the opposed seal faces (normally the outer diameter), and the opposite periphery of the opposed seal faces (typically the inner diameter) is disposed in communication with the pump fluid. The barrier gas is typically pressurized relative to the pump fluid and, in conjunction with pumping features such as grooves or the like provided on one of the opposed faces, is effective for creating a gas film between the opposed faces to maintain a small separation therebetween, while at the same time preventing the pump fluid from migrating outwardly between the opposed seal faces.
In situations where the pump fluid is a liquid, and even though the liquid is termed cleaned, it has been observed that the liquid nevertheless contains some quantity of small solid particles therein as contaminates. Further, as the technology associated with gas seals and the life of such seals continues to improve, it has been observed that the small quantity of solids contained in "clean" fluids can create a problem with respect to the gas seal. In particular, it is believed that these solid particles tend to become trapped at a fairly high level of concentration in the liquid which gains entry into the seal unit adjacent the inner periphery of the opposed seal faces, and these solids tend to cause erosion or wear of the seal members adjacent the inner periphery of the opposed seal faces.
Accordingly, it is an object of this invention to provide an improvement with respect to the overall seal construction which attempts to at least minimize the aforementioned problem.
More specifically, this invention relates to an improved gas seal construction which is particularly desirable for use on a pump to create a seal between the relatively rotatable pump shaft and housing, and which includes a shroud structure which is disposed in close surrounding relationship to the rotating shaft axially between the seal and the pump chamber, and which is effective for causing many of the solid particles in the pump liquid to be returned to the pumping chamber and thus prevent their entry past the shroud into the region adjacent the opposed seal faces.
In the improved arrangement of the invention, as briefly summarized above, the shroud comprises an annular ring which is fixed to the housing in closely surrounding relationship to the rotatable shaft, and the shroud has an inner cylindrical surface thereon which is of a generally tapered or truncated conical configuration so as to slope outwardly at a small angle relative to the shaft as the shroud projects axially away from the seal-side of the shroud toward the pump chamber. The small diameter end of the shroud, which is disposed adjacent the seal-side, has a diameter which exceeds the shaft diameter by only a small radial clearance so that the rotation of the shaft relative to the closely surrounding shroud, and the rotational effect on the pump liquid, causes the solid particles due to their greater weight to be displaced radially outwardly by centrifugal force so as to move into a position adjacent the inner truncated conical wall of the shroud, with the solid particles then flowing axially along this shroud from the small to the large diameter end thereof, thereby permitting return of many of the solid particles back to the pumping chamber.
Other objects and purposes of the invention will be apparent to persons familiar with arrangements of this general type upon reading the following specification and inspecting the accompanying drawings.